The invention relates to the preparation of biocidal formulations. Conventionally, the extermination of agricultural pests always involves the application of large amounts of chemical pesticides. It is well-known that chemical pesticides may cause pests to develop resistance to pesticides, and that residuals of pesticides often cause pesticidal pollution to the environment. Since chemical pesticides have potential danger to human beings (and animals) and the environment, the use of chemical pesticides should be judiciously controlled and the amount of usage maintained to a minimum. It is preferred to develop biocides which can selectively and effectively kill pests while they can be degraded in the environment. It is also highly preferable to develop biocides that will not cause harms to human beings and the crops.
One of the main disadvantages of biocides is that they cannot resist high temperature. If the preparation of biocidal formulations is conducted at elevated temperatures, the biocides may be destroyed or their activities substantially reduced. Therefore, conventionally, the preparation of biocidal formulation must be processed at low temperatures in order to protect biocides and to maintain the activity thereof.
R. L. Dunkle et at. disclose a method for the preparation of starch-encapsulated Bacillus thuringiensis in "Environmental Entomology" (vol. 17, PP. 120-126, 1988). In this reference, the method for the preparation of starch-encapsulated biocide is described as follows. Refined corn oil (2 g) was mixed with pre-gelatinized starch powder (25 g). Chilled distilled water (60 ml, 2.degree. C.) containing a suspension of Bacillus thuringiensis spores and crystals at a desired concentration was stirred into the starch-oil mixture to form a gelatinous mass. The mixture was allowed to stand for 30 minutes at room temperature to produce a rubbery, non-sticky mass which was processed in a blender with 25 g of starch powder to produce pesticide-containing small particles. After air dried for 24 hours at room temperature, the particles were sieved into various mesh sizes. This process, which involved cooling at room temperature for 24 hours, was employed in order to avoid the reduction of the activity of biocide due to heat or high temperature. This process is cumbersome and cannot be performed as a continuous process.